Stockholders' Equity - Summary of Changes in Stockholders' Equity (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Jan. 01, 2018
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in shares)			1,308
Balance at December 31, 2017			$ 20,501
Net income (loss)	$ 1,819	$ 3,069	3,358	$ 5,768
Other comprehensive income, net of tax	$ 172	$ (140)	130	$ (158)
Issuances under employee stock purchase plan			48
Issuances under equity incentive plans			109
Stock-based compensation			477
Repurchases of common stock			(1,580)
Dividends declared			$ (1,499)
Cumulative effect from the adoption of new accounting standards					$ 190
Ending Balance (in shares)	1,296		1,296
Balance at June 30, 2018	$ 21,734		$ 21,734
Common Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Beginning Balance (in shares)			1,308
Balance at December 31, 2017			$ 1
Issuances under employee stock purchase plan (in shares)			1
Issuances under equity incentive plans (in shares)			8
Repurchases of common stock (in shares)			(21)
Ending Balance (in shares)	1,296		1,296
Balance at June 30, 2018	$ 1		$ 1
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			1,264
Issuances under employee stock purchase plan			48
Issuances under equity incentive plans			109
Stock-based compensation			477
Repurchases of common stock			(54)
Balance at June 30, 2018	1,844		1,844
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			165
Other comprehensive income, net of tax			130
Cumulative effect from the adoption of new accounting standards					(293)
Balance at June 30, 2018	2		2
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			19,012
Net income (loss)			3,355
Repurchases of common stock			(1,526)
Dividends declared			(1,499)
Cumulative effect from the adoption of new accounting standards					$ 483
Balance at June 30, 2018	19,825		19,825
Noncontrolling Interest
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at December 31, 2017			59
Net income (loss)			3
Balance at June 30, 2018	$ 62		$ 62